Magnesium (Mg2+) is the second most abundant cation in cells. Because Mg2+ serves as a cofactor in hundreds of enzymatic reactions, it has a profound influence on many biological activities including DNA and protein synthesis, ion transport, intracellular signal transduction, and cell growth and differentiation. Consequently, it is not surprising that Mg2+ deficiency has been implicated in various disease states such as atherosclerosis, hypertension, diabetes, asthma, and alcoholism. Yet, our understanding of Mg2+ homeostasis lags far behind that of other cations such as Ca2+, Na+, K+, and H+, largely because the transporters of Mg2+ have not been identified at the molecular level. In addition, little work has been conducted concerning the effects of Mg2+ deficiency on gene expression, especially with respect to its role in various pathological conditions. Gene expression profiling using cDNA microarrays represents a powerful method for identifying genes involved in specific cellular or disease processes. We propose to use this technology to identify genes involved in magnesium homeostasis and to elucidate the mechanisms by which magnesium deficiency leads to various disease states. By comparing global gene expression patterns of select organs of normal mice to their counterparts in magnesium-deficient mice, it should be possible to identify genes involved in magnesium homeostasis, such as those encoding magnesium transporters. Genes that are aberrantly expressed under magnesium-deficient conditions should also be identified. This should lead to a better understanding of magnesium's role in health and disease. In Aims 1 and 2 commercial cDNA microarrays will be used to investigate the effects of acute and chronic magnesium deficiency on gene expression, respectively. In Aim 3 suppression subtraction hybridization libraries will be constructed from various organs of magnesium-replete and magnesium-deficient mice. Clones from the library will then be used to construct custom cDNA microarrays for gene expression profiling. This combination of techniques should lead to the identification of all genes that are differentially expressed during magnesium deficiency.